1. Field of the Invention
The present invention relates to a wireless power transmission apparatus that wirelessly transmits electric power.
2. Description of the Related Art
An electromagnetic induction system is known as a system for wirelessly feeding electric power. In recent years, a wireless power feed and charging system employing a system called magnetic resonance system that makes use of a magnetic resonance phenomenon attracts attention.
At present, in a non-contact power feeding system of the electromagnetic induction system already in wide use, a power feeding source and a power feeding destination (a power receiving side) need to share magnetic fluxes. It is necessary to arrange the power feeding source and the power feeding destination extremely close to each other to efficiently feed electric power. Further, axis alignment for coupling is important.
On the other hand, in a non-contact power feeding system that makes use of the magnetic resonant phenomenon, because of the principle of the magnetic resonance phenomenon, there are advantages that power transmission can be performed with a power feeding source and a power feeding destination arranged farther apart from each other than those in the electromagnetic induction system and transmission efficiency is not very deteriorated even if axis alignment is somewhat poor.
Besides the magnetic resonance system, there is also an electric resonance system as a resonance system that makes use of the electromagnetic resonance phenomenon.
For example, JP-A-2001-185939 discloses a wireless power feed system employing the magnetic resonance system.
In the technique disclosed in JP-A-2001-185939, electric power is transmitted from a power feeding coil, which is connected to a power feeding circuit, to a resonant coil by electromagnetic induction. Adjustment of a frequency is performed by a capacitor and a resistor connected to the resonant coil.
In recent years, a wireless power transmission technique is reported that, employing the magnetic resonance system that makes use of a resonance phenomenon of a magnetic field, realizes power transmission of 60 W at a distance of 2 m.
The development of a highly efficient “wireless power feed system” is reported that, employing the magnetic resonant system, transmits electric power of 60 W and drives an electronic apparatus arranged at a distance of 50 cm.
In this wireless power transmission technique, since wireless power transmission of several tens watts can be performed at a distance of several meters, the application of the wireless power transmission technique to new concept appliances in offices and homes is expected.